WASHINGTON – An Indiana man who taught sex offenders and aspiring federal law enforcement officers how to cheat their court — or job-imposed lie detector tests was sentenced to eight months in prison Friday — a somewhat muted victory for authorities hoping to send a stern warning to those in the business of beating polygraphs.

Federal prosecutors in Virginia had asked that Chad Dixon, 34, spend at least 21 months in prison, saying in court Friday that he “chose to enrich himself by teaching others how to lie, cheat and steal.” But federal district Judge Liam O’Grady seemed somewhat sympathetic to Dixon’s argument that merely teaching someone how to trick a lie detector is protected as a form of free speech, telling attorneys at one point, “There’s nothing unlawful about maybe 95 percent of the business he conducted.”

O’Grady, though, rejected Dixon’s request for no prison time, saying that Dixon “went into this business for greed” and his teachings “potentially caused a great deal of damage.” He noted that Dixon — who pleaded guilty in December to wire fraud and obstruction of an agency proceeding — went too far when he helped undercover agents learn to cheat the polygraph after they told him specifically that they intended to lie as they applied for federal jobs.

Choking back tears, Dixon, an electrical worker, told O’Grady he wished he could “turn back the hands of time.”

“Definitely one of the largest regrets of my life, bar none,” Dixon said. “If I could take it back, I would.”

Prosecutors had accused Dixon of teaching what they call “polygraph countermeasures” to as many as 100 people across the country — among them convicted sex offenders and those applying for federal law enforcement jobs. Inspired by Doug Williams, a former police polygraphist in Oklahoma who preaches about beating the test, Dixon would charge as much $1,000 for six to eight hours of hands-on training and would travel across the country to meet his customers, prosecutors said. He advertised his services online, and his instruction was sometimes as simple as “relax and breathe normally.”

“Mr. Dixon embarked upon a career of criminal deceit,” federal prosecutor Anthony Phillips said in court Friday. “This crime matters because what he did endangers others.”

Nina Ginsberg, Dixon’s attorney, argued that Dixon’s only real crime was encouraging customers to lie on federal polygraph tests about whether they had received countermeasures training. She said Dixon, who was struggling financially and generally disliked polygraph tests, tried to avoid training people who might pose a danger to the community.

“This is not an evil man,” Ginsberg said. “This is a very decent man who made bad choices in the context of very ill-defined law.”

Prosecutors said authorities were first tipped to Dixon’s business in April 2011, when a Customs and Border Protection applicant caught using polygraph countermeasures told investigators he had learned them from Dixon. Investigators eventually sent in undercover agents to “see just how far Mr. Dixon was willing to go,” Phillips said. He said that one agent told Dixon he was having a sexual relationship with an underage girl, and Dixon responded that he did not care because the girl was not his own daughter.

The McClatchy news organization reported last month that Dixon’s case was part of a broader federal effort to discourage possible criminals and spies from getting government jobs using polygraph countermeasures. The case also reignited a national debate on the accuracy of polygraph testing — a debate that played out in court Friday, when O’Grady seemed to deride the accuracy of the tests.

“They’re very useful tools,” O’Grady said, “until you turn the machine on.”